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Comments on and re-evaluation of the paper “18O/16O ratio measurements of inorganic and organic materials by elemental analysis-pyrolysis-isotope ratio mass spectrometry continuous-flow techniques” by Fourel et al. (2011) Rapid Commun. Mass Spectrom. 25, 2691-2696
No full textSeasonal variation in carbon isotopic composition of bog plant litter during 3 years of field decomposition
No full textIn this study, we describe the seasonal variation in 13C abundance in the litter of two Sphagnum species and four vascular plant species during 3 years of field decomposition in an Italian alpine bog. Litter bags were periodically retrieved at the end of summer and winter periods, and the δ13C in residual litter was related to mass loss, litter chemistry, and climatic conditions. In Sphagnum litter, higher rates of decomposition during summer months were associated with an increase of δ13C probably due to the incorporation of microbial organic compounds rich in 13C in the residual litter. In the litter of Eriophorum vaginatum, Carex rostrata and Calluna vulgaris, we observed a decrease of δ13C with an increase in the concentration of lignin-like compounds. The residual litter of Potentilla erecta showed a decrease of 13C abundance during the first 2 years, but on proceeding the decomposition, the δ13C increased again probably reflecting the incorporation of microbial organic compounds. © Springer-Verlag 2009
Continuous-flow δ18O measurements: New approach to standardization, high-temperature thermodynamic and sulfate analysis
No full textThe continuous-flow method for the determination of the O-isotope composition of solid samples has significant advantages over off-line extraction methods, but the problem has arisen of the standardization of results that has only partially been resolved by the use of water standards. We propose a new approach to standardization that uses carbothermic reduction of calcium carbonate standards catalyzed by high-purity AgCl. Analytical accuracy, precision, variance homogeneity and long-term stability are proven. Preliminary data on the barium sulfate δ18O analyses are reported, with a closer look at the different results obtained by off-line and on-line methods on intercomparison standards NBS-127 and MSS3. Copyright © 2005 John Wiley & Sons, Ltd
Seasonal variation in carbon isotopic composition of bog plant litter during 3 years of field decomposition
No full textIn this study, we describe the seasonal variation in
13C abundance in the litter of two Sphagnum species and four vascular plant species during 3 years of field decomposition in an Italian alpine bog. Litter bags were periodically retrieved at the end of summer and winter periods, and the δ13C in residual litter was related to mass loss, litter chemistry, and climatic conditions. In Sphagnum litter, higher rates of decomposition during summer months were associated with an increase of δ13C probably due to the incorporation of microbial organic compounds rich in 13C in the residual litter.
In the litter of Eriophorum vaginatum, Carex rostrata and Calluna vulgaris, we observed a decrease of δ13C with an increase in the concentration of lignin-like compounds. The residual litter of Potentilla erecta showed a decrease of 13C abundance during the first 2 years, but on proceeding the decomposition, the δ13C increased again probably reflecting the incorporation of microbial organic compounds
δ18O of carbonate, quartz and phosphate from belemnite guards: Implications for the isotopic record of old fossils and the isotopic composition of ancient seawater
No full textBelemnite guards of Cretaceous and Jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum. The oxygen isotopic composition of coexisting carbonate, quartz and phosphate from the same rostrum was measured according to well-established techniques. None of these compounds showed isotopic values in equilibrium with one another. Assuming δ18O values of the diagenetic water within the range of meteoric waters, the δ18O(SiO2) yield temperatures in agreement with the apparent secondary origin of this phase. The δ18O(CO2-3) range, with a certain continuity, between -10.8 and +0.97 PDB-1 with most of the intermediate values being within the range of the carbonate isotopic values of Mesozoic fossils. The most positive isotopic results obtained from phosphate are close to +23/+24‰ (V-SMOW). They can hardly be related to a secondary origin of the phosphate, or to the presence of diagenetic effects, since these results are among the most positive ever measured on phosphate. As far as we know there is no widespread diagenetic process determining an 18O enrichment of phosphate. The very low concentration of phosphate did not allow the determination of its mineralogical composition. All the available δ18O(PO43-) values from belemnite and non-belemnite fossils of marine origin of Tertiary and Mesozoic age are reported along with the newly measured belemnites. The following conclusions may be drawn from the data reported: (1) the pristine oxygen isotope composition of fossil marine organisms (either carbonate or phosphate) may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water; this process is apparent even in the case of geologically recent fossils; (2) the δ18O(PO43-) of belemnite rostra seems to be, at least in the case of the most positive results, in isotopic equilibrium with environmental water because of the similarity between the results from Cretaceous belemnites and the results from Cretaceous and Lower Tertiary pelecypods and fish teeth; 3) if so, the only feasible interpretation that can be suggested for the 18O enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from Jurassic to recent time. © 2002 Elsevier Science B.V. All rights reserved
Microtus (Tyrrhenicola) henseli del Pleistocene medio e superiore della Sardegna occidentale: morfologia, biocronologia e dati isotopici
No full textBedrock geology interacts with altitude in affecting leaf growth and foliar nutrient status of mountain vascular plants
No full textAims: Altitude is often used as a proxy for ascertaining how warming affects plant growth and leaf level properties. However, we have a poor understanding of how the effects of altitude-related warming varies across geology. Therefore, this study examined the independent and interactive effects of altitude and geology and species on plant growth and foliar nutrient status. Methods: We determined leaf growth rates and concentrations of major nutrients (nitrogen, N and phosphorus, P) in leaves of five species across two altitudinal gradients (1200-2200 m) in the Dolomites (south-eastern Alps, Italy). The two transects were located on carbonate bedrock and silicate bedrock, respectively. We also determined concentrations of inorganic and organic N and P forms in soils, and δ 15N signature in leaves and soils. Important Findings: Foliar N concentrations were unrelated to bedrock geology. The negative foliar δ 15N signature suggested that organic N was the primary source of N supply across the gradients. Foliar P concentrations were strongly affected by bedrock geology and their altitudinal patterns depended on the concentrations of organic and inorganic P forms in the soil. Phosphates and organic P appeared to be the main sources of P supply. Leaf growth rates increased with higher altitude on silicate bedrock and decreased with higher altitude on carbonate bedrock and presented a significant positive correlation with foliar N:P. In conclusion, bedrock geology interacted with altitude in controlling the foliar nutrient status mainly owing to availability of soil Pand its effect on foliar nutrient stoichiomctry
87Sr/86Sr Isotope Ratio as a Tool in Archaeological Investigation: Limits and Risks
No full textDuring the last forty years, the use of strontium isotopes in archaeology and biogeochemical research has spread widely. These isotopes, alone or in combination with others, can contribute to trace past and present environmental conditions. However, the interpretation of the isotopic values of strontium is not always simple and requires good knowledge of geochemistry and geology. This short paper on the use of strontium isotopes is aimed at those who use this tool (archaeologists, but not only) but who do not have a thorough knowledge of mineralogy, geology, and geochemistry necessary for a good understanding of natural processes involving these isotopes. We report basic knowledge and suggestions for the correct use of these isotopes. The isotopic characteristics of bio-assimilable strontium depend not so much on the isotopic characteristics of the bulk rock as, rather, on those of its more soluble minerals. Before studying human, animal and plant remains, the state of conservation and any conditions of isotopic pollution should be carefully checked. Samples should be collected according to random sampling rules. The data should be treated by a statistical approach. To make comparisons between different areas, it should be borne in mind that the study of current soils can be misleading since the mineralogical modification of soil over time can be very rapid
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